The invention relates to an electrode and to a fuel cell stack for a fuel cell with self-supporting properties.
A high temperature fuel cell (SOFC) consists of a fuel cell stack and the associated peripheral equipment. A fuel cell stack includes a plurality of units comprising an electrolyte, a cathode and an anode. The electrolyte consists for example of yttrium-stabilized zirconium dioxide (YSZ) (ZrO.sub.2 -8 mol % Y.sub.2 O.sub.3), the cathode consists for example of strontium-doped lanthanum manganese oxide (LSM) (La.sub.1-x-y Sr.sub.x MnO.sub.3-z) and the anode consists for example of a catalytically not effective and a catalytically effective phase (for example Nickel-YSZ Cermet; 40 Vol-% Ni/60-Vol-% YSZ). Interconnector plates connect several anode-electrolyte-cathode units with one another.
From the German patent application No. 195 19 847.6-45, it is known to employ self-supporting electrolyte foils and interconnector plates.
The term self-supporting property means that the foils do not bend if they are lifted at one point. The two electrodes are deposited on the electrolyte foil as layers. The electrolyte foils as well as the interconnector plate must insure the mechanical stability.
It is necessary that the self-supporting electrolyte foil has a thickness of about 200-300 .mu.m in order to insure the mechanical stability. However, a thick electrolyte layer inhibits the ion transport through the electrolyte which occurs in the fuel cells.
In order to eliminate this disadvantage, the substrate concept has been developed. A porous substrate is prepared from one of the electrode materials and is used as support for the other cell components. It must be made accordingly thick. Requiring a layer thicknesses of more than 0.5 mm, since the porous layer has a much smaller strength than, for example, the electrolyte.
On this substrate, a very thin electrolyte layer is deposited and the second electrode layer is deposited thereon. These three-layer cell units together with the interconnector plates are connected in series to form a stack.
It is a disadvantage of both these concepts that expensive materials such as YSZ, cerium-compounds or lanthanum compounds must be used for the manufacture of the self-supporting components.
It is the object of the invention to provide an electrode and a fuel cell stack by which the disadvantages mentioned are minimized.